Monolayers of ether lipids from archaebacteria

The surface behavior of six different ether lipids from archaebacteria, based on condensation of glycerol or more complex polyols with two isoprenoid alcohols at 20 or 40 carbon atoms, was investigated in monolayers at the air-water interface.The compounds with no complex polar group (GD, GDGT, GDNT) form monolayers showing a reversible collapse at surface pressure as low as 22 dynes/cm. This collapse pressure decrease with temperature in such a way that the film tension remains constant. In condensed films, these molecules do not assume a completely upright position.Lipids with complex polar ends (HL, GLB, PLII) form films more stable to compression. Forcearea characteristics and surface moment values of HL monolayers are similar to those of analogous ester lipids with fatty acid chains. Monolayers of the two bipolar lipids, GLB and PLII, at room temperature present a more condensed state, probably due to the lateral cohesion between long alkyl chains, but a lower collapse pressure.For all bipolar lipids, the area expansion induced by temperature increase is larger than that of monopolar ones.Abbreviations GD Glycerol diether (2,3-di-O-phytanyl-sn-glycerol - GDGT Glycerol-dialkyl-glycerol tetraether - GDNT Glycerol-dialkyl-nonitol tetraether - GLB Glycolipid B - PLII Phospholipid II - HL Total lipid extract from Halobacterium halobium     

Exogenous ether lipids predominantly target mitochondria

Ether lipids are ubiquitous constituents of cellular membranes with no discrete cell biological function assigned yet. Using fluorescent polyene-ether lipids we analyzed their intracellular distribution in living cells by microscopy. Mitochondria and the endoplasmic reticulum accumulated high amounts of ether-phosphatidylcholine and ether-phosphatidylethanolamine. Both lipids were specifically labeled using the corresponding lyso-ether lipids, which we established as supreme precursors for lipid tagging. Polyfosine, a fluorescent analogue of the anti-neoplastic ether lipid edelfosine, accumulated to mitochondria and induced morphological changes and cellular apoptosis. These data indicate that edelfosine could exert its pro-apoptotic power by targeting and damaging mitochondria and thereby inducing cellular apoptosis. In general, this study implies an important role of mitochondria in ether lipid metabolism and intracellular ether lipid trafficking.     

Dibiphytanyl ether lipids in nonthermophilic crenarchaeotes

[This corrects the article on p. 1136 in vol. 64.].     

Stereochemical specificity of the biosynthesis of the alkyl ether bond in alkyl ether lipids.

The stereochemical course of the formation of the alkyl ether bond in alkyl ether lipids was investigated through the synthesis of stereospecifically labeled acyl R- or S-[1-3H]dihydroxyacetone 3-phosphate (DHAP) starting from L-glyceraldehyde. It was demonstrated directly that the formation of the alkyl ether bond results in the stereospecific exchange of the pro-R C-1 hydrogen of DHAP with a proton of water. The configuration of the hydrogen that is retained on C-1 after formation of the alkyl ether bond was also investigated. The alkyl ether lipid was degraded, and the DHAP backbone isolated as glycerol, converted to DHAP via glycerol 3-phosphate and treated with either aldolase or triose phosphate isomerase. The results demonstrated that the retained hydrogen on C-1, which was pro-S in the starting substrate, was pro-S in the product alkyl ether.     

Structural and functional roles of ether lipids

Ether lipids, such as plasmalogens, are peroxisomederived glycerophospholipids in which the hydrocarbon chain at the sn-1 position of the glycerol backbone is attached by an ether bond, as opposed to an ester bond in the more common diacyl phospholipids. This seemingly simple biochemical change has profound structural and functional implications. Notably, the tendency of ether lipids to form non-lamellar inverted hexagonal structures in model membranes suggests that they have a role in facilitating membrane fusion processes. Ether lipids are also important for the organization and stability of lipid raft microdomains, cholesterol-rich membrane regions involved in cellular signaling. In addition to their structural roles, a subset of ether lipids are thought to function as endogenous antioxidants, and emerging studies suggest that they are involved in cell differentiation and signaling pathways. Here, we review the biology of ether lipids and their potential significance in human disorders, including neurological diseases, cancer, and metabolic disorders.     

Regularity of isoprenoid biosynthesis in the ether lipids of archaebacteria

The location of paired and unpaired ¹³C atoms in the 16,16′-biphytanyl components of the lipids of Caldariella acidiophila following incorporation of acetate-[1,2-¹³C₂] shows that the overall process of isoprenoid biosynthesis in this archaebacterial species follows a normal pattern and that the head-to-head linkage of the two tetraprenyl chains occurs stereoselectively.     

Signalling steps in apoptosis by ether lipids

We have investigated the mechanisms of induction of apoptosis by the antineoplastic ether lipid ET-18-OCH₃ (ALP) in sensitive S49^wt mouse lymphoma cells and ALP-resistant S49^ar variants, both with wild-type p53, and in related L1210 cells with mutated p53. Ether lipid-resistant S49^ar cells were cross-resistant to extracellular stress factors (cold shock, heat shock, H₂O₂, dimethylsulfoxide) and to radiation-induced apoptosis but not to physiological apoptotic signals (dexamethasone, growth factor deprivation, thapsigargin, C₂-ceramide) and expressed similar levels of the apoptosis-regulating proteins Bcl-2, Bcl-X, Bax, Bad and Bak as did the parent S49^wt cells. The uptake of [³H]-ALP was strongly reduced in the stress-resistant cells but this was not associated with significant differences in membrane cholesterol:phospholipid content nor in membrane microviscosity. In S49^ar cells the activity of the antioxidant enzyme glutathione peroxidase (GSH-Px) was increased 4-fold and depletion of glutathione with the drug L-buthionine-S-R-sulfoximine (L-BSO) lowered the resistance of S49^ar cells to ALP, stress factors and ionising radiation. The results indicate that ether lipids induce apoptosis by imposing a special form of physico-chemical stress, mediated by reactive oxygen species but independent of p53 status. The capacity of glutathione-dependent anti-oxidant defence appeared an important and shared determinant of the sensitivity to ether lipids, several types of extracellular stress and ionising radiation.     

Synthesis and chiroptical properties of neutral ether lipids

A variety of neutral ether lipids was synthesized. A method for the synthesis of 1,3-O-dialkyl-sn-glycerols was developed which involves selective alkylation of 3-O-alkyl-sn-glycerols. The ORD and CD curves of the various glyceryl ethers and their esters were analyzed. The correlation between the CD sign of the acyl residue and its position in the glycerol derivative was clarified.     

NMR spectral analysis of cytotoxic ether lipids.

Several cytotoxic ether lipid analogs of platelet activating factor exhibit a wide range of interesting pharmacological properties. Furthermore, at least two members of this family of lipids have progressed to phase I clinical trials as potential cancer chemotherapeutic agents. In spite of the promise that these compounds hold as anticancer drugs, they remain poorly characterized. We report herein the first complete 1H NMR analysis of several palmityl-based ether lipids. In addition, we report the 13C NMR spectral assignments for these lipids, which are based, in part, on both the presence and magnitude of 31P-13C and 14N-13C coupling constants.     

Chain substituted polymerizable ether lipids: synthesis of sorbyl and diacetylenic ether glycerophosphocholine.

Three novel polymerizable ether lipids, 1,2-O-bis[10(2',4'-hexadienoyloxy)decyl]-rac, 1,2-O-bis(10,12-tricosadiynyl)-rac, and (-)-2,3-O-bis(10,12-tricosadiynyl)-sn-glycero-1-phosphocholine, were synthesized from 3-O-benzyl-rac, 3-O-trityl-rac and (-)-1-O-trityl-sn-glycerol as starting materials, respectively. All the reactions employed in these multi-step syntheses are straightforward giving an overall yield of 21% for the sorbyl, 42% for the racemic diacetylenic and 44% for the chiral diacetylenic lipid. All the lipids form bilayer assemblies on hydration and show transitions from gel to liquid-crystalline phases at 11.4 degrees, 27.6 degrees and 30.0 degrees C, respectively. Bilayer assemblies of each are photoreactive and are readily polymerized by irradiation with 254 nm light. Tubules of the chiral diacetylenic ether lipid were observed.     

Stability of pressure-extruded liposomes made from archaeobacterial ether lipids

Ether lipids were obtained from a wide range of archaeobacteria grown at extremes of pH, temperature, and salt concentration. With the exception ofSulfolobus acidocaldarius, unilamellar and/or multilamellar liposomes could be prepared from emulsions of total polar lipid extracts by pressure extrusion through filters of various pore sizes. Dynamic light scattering, and electron microscopy revealed homogeneous liposome populations with sizes varying from 40 to 230 nm, depending on both the lipid source and the pore size of the filters. Leakage rates of entrapped fluorescent or radioactive compounds established that those archaeobacterial liposomes that contained tetraether lipids were the most stable to high temperatures, alkaline pH, and serum proteins. Most ether liposomes were stable to phospholipase A2, phospholipase B and pancreatic lipase. These properties of archaeobacterial liposomes make them attractive for applications in biotechnology.     

A method for the separation and characterization of archaebacterial signature ether lipids

A reproducible high performance liquid chromatography (HPLC) method for the separation of diethers and tetraethers isolated from archaebacterial phospholipids is reported. Fourier transform infrared spectroscopy was used for structural confirmation of these signature lipids. A mixture of tetraethers from a thermoacidophilic archaebacteria was resolved into three major components by the normal phase separation. These components were differentiated by Fourier self-deconvolution of infrared spectra. The application of the HPLC technique to environmental samples may provide an accurate assessment of archaebacterial biomass in various microbial communities.     

A range of ether core lipids from the methanogenic archaebacterium Methanosarcina barkeri

The core ether lipids of the methanogenic archaebacterium Methanosarcina barkeri were found to consist of C₂₀,C₂₀ glycerol diether and trace amounts of C₂₀,C₂₅ glycerol diether, C₂₀ glycerol monoether, C₄₀,C₄₀ diglycerol tetraethers with 1–3 cyclopentane rings, and a novel C₂₀,C₂₀ tetritol diether.     

Structure and polymorphism of bipolar isopranyl ether lipids from archaebacteria

We describe in this work the structure and polymorphism of a variety of lipids extracted from Sulfolobus solfataricus, an extreme thermoacidophilic archaebacterium growing at about 85 °C and pH 2. These lipids are quite different from the usual fatty acid lipids of eukaryotes and prokaryotes: each molecule consists of two C₄₀ ω-ω′ biphytanyl residues (with 0 to 4 cyclopentane groups per residue), ether linked at both ends to two (variably substituted) glycerol or nonitol groups. Four lipid preparations were studied; the total and the polar lipid extracts, and two hydrolytic fractions, the symmetric glycerol dialkyl glycerol tetraether and the asymmetric glycerol dialkyl nonitol tetraether, as a function of water content and temperature, using X-ray scattering techniques. The main conclusions from the study of the four lipid preparations can be summarized as follows. (1) As with other lipids, a remarkable number and variety of phases are observed over a temperature-concentration range close to “physiological” conditions. The possibility is discussed that this polymorphism reflects a fundamental property of lipids, closely related to their physiological rôle. (2) As in other lipids, two types of chain conformations are observed: a disordered one (type α) at high temperature; at lower temperature, a more ordered packing of stiff chains, all parallel to each other (type β′). At temperatures and degrees of hydration approaching the conditions prevailing in the living cell, the conformation is of type α. (3) In all the phases with chains in the α conformation, the unsubstituted glycerol headgroups, whose concentration is high in these lipids, segregate in the hydrocarbon matrix, away from the other polar groups. This property may have interesting biological consequences: for example, the chains of a fraction of the bipolar lipid molecules can span hydrocarbon gaps as wide as 75 Å. (4) Two cubic phases are observed in the total and the polar lipid extracts, which display a remarkable degree of metastability, most unusual in lipid phase transitions involving structures with chains in the α conformation. This phenomenon can be explained by the interplay of the physical structure of the cubic phases (the two contain two intertwined and unconnected three-dimensional networks of rods) and the chemical structure of the lipid molecules: the two headgroups of most molecules being anchored on each of the two networks of rods, the migration of the lipid molecules is hindered by the two independent diffusion processes and by the entanglement of the chains. The possibility is discussed that this phenomenon may reflect an evolutionary response to a challenge of the natural habitat of these archaebacteria.     

Biologically active lipids. Semi-synthesis of 3H-labeled ether glycerophospholipids and ether glyceroglycolipids from ratfish liver oil

1-O-Alkyl-2,3-diacyl-sn-glycerols, the major constituents of ratfish (Chimaera monstrosa) liver oil, serve as starting material for the preparation of 1-O-alkyl-sn-glycero-3-phosphocholines, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholines, 1-O-alkyl-2-O-methyl-sn-glycero-3-phosphocholines, and 1-O-alkyl-2-O-methyl-sn-glycero-3-beta-D-glucopyranosides. Catalytic tritiation of the unsaturated alkyl moieties in these biologically active ether lipids affords the corresponding 3H-labeled substances.     

Novel alk-1-enyl ether lipids isolated from Clostridium acetobutylicum

Alkenyl ether analogues of phosphatidylglycerol (plasmenylglycerol), bisphosphatidylglycerol (cardiolipin) (plasmenylglycerolphosphatidic acid), monoglycosyldiglyceride and diglycosyldiglyceride were isolated from the polar lipids of Clostridium acetobutylicum and characterized by chemical analyses and degradation. The position of the alkenyl ether bond (at C-1) and of the acyl ester bond (at C-2) as well as the configuration at C-2 of the phospholipids are the same as of the alkenyl ether phospholipids known so far. The alkenyl ether analogue of monoglycosyldiglyceride contains a galactosyl residue, that of diglycosyldiglyceride a glucosyl-galactosyl residue, glucosyl forming the terminal unit.     

Organophosphate-sensitive lipases modulate brain lysophospholipids, ether lipids and endocannabinoids

Lipases play key roles in nearly all cells and organisms. Potent and selective inhibitors help to elucidate their physiological functions and associated metabolic pathways. Organophosphorus (OP) compounds are best known for their anticholinesterase properties but selectivity for lipases and other targets can also be achieved through structural optimization. This review considers several lipid systems in brain modulated by highly OP-sensitive lipases. Neuropathy target esterase (NTE) hydrolyzes lysophosphatidylcholine (lysoPC) as a preferred substrate. Gene deletion of NTE in mice is embryo lethal and the heterozygotes are hyperactive. NTE is very sensitive in vitro and in vivo to direct-acting OP delayed neurotoxicants and the related NTE-related esterase (NTE-R) is also inhibited in vivo. KIAA1363 hydrolyzes acetyl monoalkylglycerol ether (AcMAGE) of the platelet-activating factor (PAF) de novo biosynthetic pathway and is a marker of cancer cell invasiveness. It is also a detoxifying enzyme that hydrolyzes chlorpyrifos oxon (CPO) and some other potent insecticide metabolites. Monoacylglycerol lipase and fatty acid amide hydrolase regulate endocannabinoid levels with roles in motility, pain and memory. Inhibition of these enzymes in mice by OPs, such as isopropyl dodecylfluorophosphonate (IDFP), leads to dramatic elevation of brain endocannabinoids and distinct cannabinoid-dependent behavior. Hormone-sensitive lipase that hydrolyzes cholesteryl esters and diacylglycerols is a newly recognized in vivo CPO- and IDFP-target in brain. The OP chemotype can therefore be used in proteomic and metabolomic studies to further elucidate the biological function and toxicological significance of lipases in lipid metabolism. Only the first steps have been taken to achieve appropriate selective action for OP therapeutic agents.     

Evolution and phylogeny of old world deer

The phylogenetic pattern and timing of the radiation of Old World deer was determined based on the complete mitochondrial cytochrome b gene from 33 Cervinae taxa. Using rooted and unrooted phylogenies derived from distinct theoretical approaches, strong support was achieved for monophyly of the Old World deer with muntjacs as sister group as well as for the divergence of at least three distinct genera: Rucervus, Dama, and Cervus. The latter clade comprises what have previously been regarded as the genera or subgenera Panolia, Rusa, Cervus, Sika, and probably Przewalskium. Our data also consistently confirmed paraphyly of nominate C. elaphus and did not support the monophyly of Axis. We used these molecular phylogenies to assess the homoplastic evolution of morphological, geographical, ecological, and selected behavioural character state differences within the Cervinae. Reliable fossil calibrations, large molecular data sets, and improved dating methods are shaping a molecular time scale for the evolutionary radiation of Old World deer that occurred at the Miocene/Pliocene transition and is largely compatible with existing palaeontological evidence. Using node ages estimated from sequence data, we estimated an average per-lineage diversification rate of 0.51+/-0.1 species per million years (my) over roughly the last 6 mya.